the role of alloying elements in steel

In order to improve and improve certain properties of steel and give it to some special performance, the elements added to the smelting process are referred to as alloying elements. Common alloy elements include chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, silicon, manganese, aluminum, copper, boron, and rare earth. Phosphorus, sulfur, nitrogen, etc. also play a role in some cases.

the-role-of-alloying-elements-in-steel

 

(1)Chromium can increase the hardness of steel and have secondary hardening effect, improve the hardness and wear resistance of carbon steel. When the content exceeds 12%, the steel has good high temperature antioxidant and oxidative corrosion, and the thermal strength of the steel is also increased. Chromium is the main alloy element of stainless steel acid resistant steel and heat resistant steel.

(2)Nickel can strengthen ferritic in steel and refine the pearlite, and the total effect is to increase the strength and the impact on plastics is not significant. Generally, for low carbon steels to be used in rolling steel, normal fire or annealing, a certain amount of nickel can improve the strength of steel without significantly reducing its toughness. When nickel is increasing steel strength, the damage of steel toughness, plasticity, and other processes of steel is small than other alloying elements. The steel which contain Nickel 3.5% can be used at -100 ° C, and 9% can be operated at -196 ° C.

(3)Tungsten is mainly used in steel to increase tempering stability, thermal strength, and wear resistance increased due to formation of carbides. Therefore, it is mainly used for tool steel, such as high-speed steel, hot forging mold steel, and the like. Since the addition of tungsten can significantly improve the wear resistance and cuttingability of steel, tungsten is the main element of the alloy tool steel.

(4)Vanadium have a very strong affinity with carbon, ammonia, oxygen , then form a corresponding stable compound. Vanadium is mainly present in the form of carbides in steel. Its main role is to refine the tissue and grains of steel, reduce the strength and toughness of steel. When the solid solution is dissolved in a high temperature, the hardenability is increased; in turn, if the hardenability is lowered as in the form of a carbide.

(5)Silicon can dissolves in ferrite and austenite to improve the hardness and strength of the steel, its effect only in phosphorus, manganese, nickel, chromium, tungsten, molybdenum, and vanadium. However, when silicon contains more than 3%, the plasticity and toughness of steel will be significantly reduced. Silicon energy improves the elastic limit of steel, yield strength and yield ratio (σs / σb), and fatigue strength and fatigue ratio (σ-1 / σb). This is silicon or silicon-manganese steel as a spring steel type.

(6)Manganese is a good deoxidizer and desulfurizer. The steel generally contains a quantity of manganese, which eliminates or reduces the heat of steel due to sulfur, thereby improving the thermal processability of steel.

(7)Manganese and iron forming solid solution, improve the hardness and strength of ferrite and austenite in steel; at the same time, it is also an element formed by carbide, replacing a portion of the iron atom in a carbon carbon, and manganese is reducing the critical transition temperature during steel. The role of refining the pearlite is also indirectly enhancing the effect of improving the strength of the pearlite steel. The ability of manganese stabilizes the austenite tissue is second only to nickel, and the hardenability of steel is also strongly increased. Manganese with no more than 2% is used to form a variety of alloy steels with other elements.

(8)Improve sulfur and manganese content can improve the cutting properties of steel, in easily cutting steel, sulfur is added as a beneficial element. Sulfur will deteriorate the quality of steel, under high temperature, reduce the plasticity of steel, is a harmful element, which exists in a lower melting point. The melting point of the FES existing alone is only 1190 ° C, while the eutectic temperature in the steel forms a co-crystal in the steel, only 988 ° C, when steel is solidified, the vulcanized iron is set at the primary grain boundary. When the steel 1100 ~ 1200 ° C is rolled, the FeS on the grain boundary will melt, greatly weaken the binding force between the grains, causing the brittle phenomenon of steel, so that the sulfur should be severely controlled. Generally controlled at 0.020% to 0.050%. To prevent brittleness caused by sulfur, sufficient manganese should be added to form a MNS having a high melting point. If the flow content is high in the steel, the gas hole and loose are formed in the weld metal due to the production of SO2 during welding.

(9)Phosphorus is added to the low alloy structural steel to improve its strength and steel resistance, but reduce its cold stamping performance. Phosphorus and sulfur and manganese can increase the cutting properties of steel, increase the surface quality of the processing member, for easy cutting steel, so that the chipping steel contains a relatively high phosphorus. Phosphorus is used for ferrite, although the strength and hardness of steel can be improved, the biggest harm is severe, and the segregation is severe, and the tempering is brittle, and the plasticity and toughness of the steel are significantly increased. Phenomenon. Phosphorus is also adversely affected. Phosphorus is harmful to elements, should be severely controlled, general content is not more than 0.03% to 0.04%.